I had a right hydrocele repair undertaken 4 weeks ago. Actual testicle is now the size of a lemon. When will it reduce in size?

Hydrocoele. If the hydrocoele is removed the testicle should be small in size - i assume by being a lemon size it is bigger. If this is the case then it could be a hematoma - i would re-visit the surgeon is have him take a look at it.
See below. Persistent enlargement on the side of the repaired hydrocele not uncommon. Most often related to inflammation, recurrent fluid, or hematoma (collection of blood) that usually resolve with time (1-3 months), anti-inflammatory meds, and occasional fluid aspiration; less likely infection requiring antibiotics; and rarely vascular compromise of testicle. Discuss with surgeon. Consider ultrasound. .